The present invention relates to a catalyst for purifying exhaust gases from internal combustion engines by oxidation and/or reduction. The catalysts can contain the platinum group metals platinum, palladium, or rhodium, separately or in combination, as is known in the art. Depending upon composition, catalysts of the invention can be used as an oxidation catalyst, as a reduction catalyst of a two-bed catalytic converter (here, the exhaust gas is first lead to a reduction catalyst and then after addition of air, to an oxidation catalyst) or as a multifunctional catalyst for the concurrent conversion of oxidizable and reducible components in the exhaust gas.
Against a background of fuel economy, modern engine designs predominantly have operation phases designed with an oxygen excess, so that catalysts with improved lean activity are increasingly required The lean activities of conventional catalysts frequently prove to be inadequate in the above mentioned engine designs For this reason, there was urgent need to remedy this deficiency.
The present invention proceeds from what is known in the teaching of West German patent (DS-PS) 29 07 106. This prior art describes exhaust gas purification catalysts, which contain platinum, rhodium, and nickel if necessary, as the active phase on a carrier made of Al.sub.2 O.sub.3 of the transition series, the said carrier having been modified by addition of CeO.sub.2, Fe.sub.2 O.sub.3, and ZrO.sub.2. The present invention expands this teaching relative to possible noble metals for active phases and the combinations thereof, and adds to the base metal components previously used therewith a new element that must be used. The present invention leads to the object of increasing lean stability and providing a type of catalyst that is universal for the oxidation and/or reduction of exhaust gases produced by internal combustion engines.